1. Field of the Invention
The present invention relates to a photoacoustic image generation method, that is, a method of emitting light toward a subject and imaging the subject based on acoustic waves generated from a part of the subject that has received the light.
In addition, the present invention relates to an apparatus for implementing such a photoacoustic image generation method.
2. Description of the Related Art
As conventionally disclosed in, for example, JP2005-021380A and JP2011-217767A, a photoacoustic imaging apparatus for imaging the inside of a living body using the photoacoustic effect has been known. In this photoacoustic imaging apparatus, pulsed light, such as pulsed laser light, is emitted to the living body. Inside the living body to which the pulsed light has been emitted, the volume of the living tissue that has absorbed the energy of the pulsed light increases due to heat, and acoustic waves are generated. Therefore, it is possible to detect the acoustic waves using detection means, such as an ultrasound probe, and visualize the inside of the living body based on the electrical signal (photoacoustic signal) obtained by the detection.
Since the photoacoustic imaging apparatus forms an image based only on the acoustic waves emitted from a specific light absorber, the photoacoustic imaging apparatus is suitable for imaging a specific tissue in the living body, for example, a blood vessel.
On the other hand, as disclosed in, for example, JP2005-342128A and JP2006-055407A, an insertion operation for collecting tissues or injecting drugs using an insertion needle inserted into the living body has been known. When performing the insertion operation, it is required to be able to grasp the position of the insertion needle, especially, the distal end position by imaging it during the operation so that organs, tissues, and the like inside the living body are not damaged by the distal end of the insertion needle.
As a method of responding to the request, as conventionally disclosed in JP2005-342128A and JP2006-055407A, there has been known a method of displaying a part of a living body including an insertion needle on an ultrasound image so that the position of the insertion needle can be checked on the image. In such a method, however, there is a problem that, in a case where the insertion needle deviates from the scanning plane (scanning cross section) on which the insertion needle is being observed, it is difficult to check the insertion needle.
Therefore, JP2005-342128A proposes a method of generating an ultrasound image for a plurality of scanning cross sections and regarding a scanning cross section having the highest reflection brightness as a cross section through which the distal end of the insertion needle passes. JP2006-055407A proposes a method of determining the deviation of the insertion needle from the scanning cross section based on the difference between the amount of movement of the distal end of the insertion needle and the amount of movement of the insertion needle between the frames of an ultrasound image. JP2013-027513A discloses a method of displaying an insertion needle on a photoacoustic image so that the position of the insertion needle can be checked on the photoacoustic image.